Gyroscopic mass flowmeter



United States Patent GYROSCOPIC MASS FLOWMETER Michael D. Altfillisch,Canton, Howard A. Powers, Medfield, and Roby B. White, Sharon, Mass.,assignors, by mesne assignments, to Detroit Controls Corporation,Detroit, Mich, a corporation of Michigan Application September 7, 1954,Serial No. 454,485 8 Claims. (Cl. 73-194) This invention relates toflowmeters and more particu larly to an improved mass flowmcter of theclass described in the co-pending applications of George S. Cherniak etal., Scr. No. 3%,414, filed September 16, 1953, now abandoned, andMichael D. Altfillisch et al., Ser. No. 454,487, filed September 7,1954.

In recent years great effort has been applied to the development of massflowmeters capable of dependably rendering highly accurate mass flowmeasurements. Most recently flowmeters employing gyroscopic principleshave received particular attention, and many discoveries have been madeto enhance their accuracy. More particularly it has been determined thatseparation of the fluid particles in heterogeneous mixtures ingyroscopic flowmetcrs produces inaccurate mass flow measurements unlesssome means is provided to restrict the separation to inactive portionsof the spinning conduit. Furthermore, certain balance requirements havebeen found necessary to eliminate density sensitivity which otherwiseintroduces errors into the measurement of mass flow.

The invention disclosed in this application was made in an effort toovercome what has proved to be another major source of error in themeasurement of mass flow.

It has been discovered that when a heterogeneous fluid or any fluidcontaining vapor is subjected to centrifugal force by rotation about anaxis, the heavier particles of the fluid move under the influence ofthat force to a position remote from the axis of rotation while thelighter particles of fluid are displaced by the heavier particles andare moved inwardly toward the drive axis. This discovery as it effectsflowmeters may best be illustrated by a more detailed description ofthis phenomenon in a conduit disposed radially with relation to its axisof rotation. If fluid composed of a mixture of air and water isintroduced into the conduit, the particles of water will move to theradial extremity of the tube, while the air therein will, in reaction tothe displacement by the water, move toward the axis. If the fluidmixture is considered to be flowing in a radially outward directionthrough the conduit under the influence of a pressure head, theparticles of air will collect in the tube between the terminal portionsthereof, and remain at that location under the influence of the opposingforces of the pressure head of the fluid and the centrifugal effect asdescribed above. The air so affected collects in the form of awedgedshaped bubble at one side of the conduit and partially interruptsthe fluid flow therethrough. Obviously, the fluid is thereby directedagainst the opposite wall of the conduit and exerts a force at thatlocation having a component perpendicular to the axis of said conduit.

If, however, the flow through the conduit is confined to a radiallyinward direction, it becomes apparent that the movement of the air willbe in the same direction as that of the water. The centrifugal action ofthe Water on the air an the pressure head of the fluid will act in thesame di tion, and accumulations of the lighter particles oi fl in theconduit will be eliminated.

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The primary object of the invention. therefore. is to prevent theaccumulation of air in the radial arms of the sensing loop of agyroscopic flowmetcr, v 'nhou't the aid of bleeds or other relief meansconnected thereto.

in the accomplishment of this and other objects we provide as oneimportant feature of this invention a sensing conduit having the flowthrough the active arms thereor' confined to a substantially radiallyinward direction about the drive axis.

These and other objects and features may be better understood andappreciated from the following detailed description of a preferredembodiment of our invcntion selected for purposes of illustration andsluilwn in the accompanying drzuving in which:

Fig. l is an inside elevation of a gyroscopic mass flowmetcr constructedin accordance with this invention.

Fig. 2 is a view in a section of the flowmeter shown in Fig. l, and

Fig. 3 is a fragmentary view of an active leg of a sensing coilillustrating the effect of radially outward flow therein.

Proceeding now to a detailed description of the embodiment of theinvention illustrated in the drawings, and a demonstration of theadvantages derived therefrom, the flowmeter is seen to comprisegenerally a sensing coil 19, an inlet conduit 12 and an outlet conduitit. A pair of bellows 16 and 18 are observed to connect the conduits tothe sensing coil and serve to direct throt h the sensing coil all of thefluid vi hose moss flow rah is to be measured. A pair of rigid supportmembers 20 rotatably carry the inlet and outlet conduits and permitrotation of the sensing coil about the drive or precession axisindicated in Fig. l. A motor 22 connected by means of a belt 24 to apulley 26 mounted on the inlet conduit 12 rotates the sensing coil inthe manner indicated above.

The sensing coil 10 will now be described in detail. An inspection ofthe drawing reveals that fluid entering the sensing coil from the inletconduit through the bellows 16 passes into a horizontal arm 28 which isperpendicular to and whose axis intersects the torque axis. The arm 28is observed to extend throughout its length substantially parallel tothe drive axis. The fluid is then directed radially inwardly toward thedrive axis by a radial leg 30 and is returned to the torque axis by asecond arm 32 whose axis is parallel to the drive axis. The fluid flowthrough the coil is subsequently directed radially outward through aconduit 34 coaxially disposed on the torque axis.

A conduit 36 formed substantially in a semi-circle with its center onthe drive axis and connected to the outer terminal end of the conduit 34carries the fluid from the first portion of the coil to a similarlyarranged porlion having a first horizontal arm 38, a radially inwardlyconducting conduit 40 and a second horizontal conduit 42. which, throughthe connecting bellows 18 directs the fluid out of the sensing coil andinto the outlet conduit 14.

Flowmeters of the class illustrated are governed by the operativeequation T =21rR QW where T is the gyroscopic couple produced about thetorque axis, R is the radius of a circumscribed circle intersecting theouter radial extremes of the active legs 30 and 40, o is theprecessional velocity in radians/sec. about the drive axis and W is themass flow rate in slugs/sec. It is obvious that the quantity 9 in theequation may either be maintained substantially constant by the use of asynchronous motor to rotate and induce precession of the coil or it mayreadily be determined by a tachometer or drag-cup or direct-currentgenerator regardless of the means employed to rotate and induceprecession of the coil. Therefore, by measuring the torque about thetorque axis, the mass flow rate W may be determined.

Before proceeding to a description of the means provided to measure thegyroscopic couple produced about the torque axis, the necessity forrestricting the flow in the active legs 30 and 40 to a radially inwarddirection will be graphically demonstrated. Fig. 3 has been presentedfor this purpose. If, for example, the active leg 30 of the sensing coilillustrated in Fig. 1 extended across the drive axis as does the conduit44 of Fig. 3, and flow therethrough of a fluid containing vapor wereconfined to the direction indicated, the centrifugal force created byrotation of said conduit about the drive axis in hte direction of thearrow would cause a wedge-shaped bubble to collect against the side ofthe tube as suggested at 46. As set forth in the introductoryparagraphs, the vapor pocket or bubble collects at the locationindicated under the influence of the pressure head of the flowing fluidand the displacement forces of the heavier particles of the fluid underthe influence of the centrifugal force.

The exact position of the bubble is obviously determined by the balanceof those forces. Because the bubble moves when changes occur in eitherof the forces, it becomes apparent that bleeder methods for disposing ofthe bubble are not satisfactory.

Continuing with an analysis of the fluid flow through the conduitillustrated in Fig. 3, the vector F1 represents the force applied by theangularly moving pipe on the fluid. The fluid flow around the bubble 46has also been illustrated in vector form, F2 representing the momentumof the cross flow of fluid acting on the pipe while vector F3 representsthe radially outward fluid flow. It is apparent, therefore, that thepresence of the bubble 46 reduces the total force applied to the movingfluid, resulting in the introduction of a negative error into the torquemeasurement made about the torque axis.

Referring now to Fig. 1, it will be appreciated that radially outwardflow has been restricted to only those portion of the coil that areineflective in the production of a torque about the torque axis. Thoseportions of the coil may be referred to as inactive legs. Specifically,radially outward flow in the leg 34 does not produce a torque about thetorque axis for the flow therethrough is coaxial with said axis.Therefore, although a vapor pocket may form between the ends of the leg34, any force applied against the side of the conduit by the fluidtherein will radiate from the torque axis. Obviously, the presence of anair or vapor pocket in the leg cannot affect the torque measured.

Flow through he semi-circular conduit 36 also fails to affect the totaltorque response about the torque axis, for the fluid passing throughsaid conduit remains in the plane of the torque axis and a fixeddistance from the drive axis. Obviously, therefore, the precession ofthe coil does not produce a tangential acceleration in the conduit 36 toaffect that torque. The conduit 36, in addition to providing fluidcommunication between the two segments of the sensing coil, performs asecond very important function, namely, it provides centrifugal balanceof the entire sensing coil about the torque axis. The necessity for sucha balance has been graphically demonstrated in the above namedco-pending applica tion r-f Altfillisch et al. Suflice it to state thatthe couple about the torque axis produced by the centrifugal forces ofthe displaced and rotating major segments of the sensing coii isbalanced by the centrifugal forces created by said rotation of thedisplaced semi-circular conduit as. Because no extraneous forces areexerted about the torque axis, the total torque is equal to thegyroscopic couple about that axis.

Proceeding now to a description of the means emloyct'. to measure thetotal torque, a gimbal 48 is observed to be mounted on the inlet andoutlet conduits if. and 14 respectively and rotates with the sensingcoil. A pair of torque bars 50 and 51 rigidly secured at their outerends to the gimbal have their inner ends fastened to the displaceablesensing coil 10. Because the bars are positioned coaxially with thetorque axis, a bracket i 56 is employed to secure the inner end of bar51 to the sensing coil, for obviously the connection may not be made tobellows 16.

Strain gauges 52 are fixed on the bars and 51 and through appropriatecircuitry diagrammatically represented by conductor 54 and slip-ringassembly 56 produce a signal at the meter 58 proportional to thegyroscopic coupled exerted about the torque axis. Because the measuringmeans per se forms no part of this invention, it will not be illustratedand described in detail. A simple circuit capable of performing thefunction intended is fully described on page 18 in Electrical ResistanceStrain Gauges by Bobie and Isaac, English University Press Ltd., London.Moreover, the strain gauges may be replaced by a dynamo transformer ofthe type disclosed in the patent to Mueller, No. 2,488,734, issuedNovember 22, 1949, with equal success.

Proceeding now to a description of the flowmeters operation, a pair offluid couplings 60 are provided to connect the meter into a linecarrying fluid whose mass flow is to be measured. Upon excitation of themotor 22, the sensing coil will rotate about the drive axis in thedirection indicated. It is to be understood, however, that the motor maybe replaced by any means which will rotate the coil about the driveaxis, and the direction and speed of rotation is wholly arbitrary, foras has been suggested above, the speed of rotation may be readilydetermined and appropriate compensations made.

Continuing with the description of the flowmeters operation, the flow offluid through the sensing coil and the angular movement thereof willcause the sensing coil to displace about the torque axis under theinfluence of the gyroscopic couple. The bellows 16 and 18 permit thedisplacement of the coil about that axis without exerting appreciableresistance thereto. If the motor rotates the coil at a constant speed,the torque exerted on the torque bars 50 and 51, and indicated at themeter 58 will be directly proportional to the mass flow rate of thefluid through the coil. If, on the other hand, the motor does not rotatethe coil at a constant speed. the measured torque indicated at the meterwill be a function of both the mass flow rate and the angular velocity 2of the coil. By dividing the measured torque which is proportional tothe product of W and Q by Q, obviously the mass flow rate may readily bedetermined. The patent to Moore, No. 2,472,609, issued June 7, i949,discloses a circuit for performing the division required when a variableangular velocity 9 is introduced and further discloses the necessarymeans for integrating the mass flow rate measurement with respect totime for obtaining total flow readings.

Having thus described in detail the flowmeter and its operation,numerous modifications and variations will readily occur to one skilledin the art to which this invention pertains.

For example, although the legs 30 and 40 have been illustrated as beingradially disposed with respect to the drive axis to prevent variationsof the effective radius R of the rotating mass when heterogeneous fluidsare passed through the meter, they may respectively be formed as smoothcurves connecting the arms 28 and 32, and the arms 38 and 42. withoutloss of accuracy if homogeneous fluids are to be measured. Although theflow through the active legs 30 and 40 would no longer be radial.nevertheless, the flow would remain in the direction of the drive axis.and. therefore, the pressure head and centrifugal eflect on vaporcarried by the homogeneous fluids would be in the same direction,thereby moving it. along the fluid path. Therefore. it is not intendedth: 1* the scope of this invention be limited to the specificallyillustrated and described embodiment thereof, for obviously theinvention encompasses a much larger field. Bisical y this inventionteaches that in all flowmeters cmploying ayroscnpic or Coriolisprinciples, the fluid flow in the sensing loop must be confined to adirection toward the axis of rotation in all parts of the coil effectivein producing a gyroscopic couple, 1'. c. in all portions of the coilexcept in those portions defining a path having a constant radius fromthe drive axis, perpendicular to the torque axis, or coaxially disposedon the torque axis. This requirement must be satisfied to obtainsubstantially 100% accurate mass flow measurements.

Aside from the advantages accuracy achieved by flownieters have theillustrated configuration, other very important advantages are derived,namely, the cost of construction of the sensing coil is substantiallyless than other configurations now known, and maximum utilization ofspace is obtained.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a flowmeter, a sensing member comprising a conduit supported bygimbal means, said conduit being characterized by a plurality of legs, asubstantial portion of said conduit being formed into at least a loopand located in the plane of said gimbal means, means for supporting saidconduit for rotation about a first axis lying in the plane of saidgimbal means, drive means for rotating said conduit about said firstaxis, means forming an inlet passage and means forming an outlet passagefor directing through said conduit the fluid to be measured, and meansdisposed between said gimbal means and said loop for detectingprecessional torque tending to rotate said conduit about a second axislying in the plane of said gimbal means, said second axis beingperpendicular to said first axis, and the configuration 01 said legs ofsaid loop being such that substantially all flow of fluid in a directionparallel to said second axis and displaced therefrom is directed towardsaid first axis.

2. In a flowmeter, a substantially rigid sensing conduit formed into atleast a loop, means for directing through said conduit all of the fluidto be measured, mounting means for supporting said conduit for rotationabout an axis of rotation in a reference plane, drive means for rotatingsaid conduit about said axis of rotation, and flexible fluid couplingsfor connecting said conduit with said first named means for permitting asmall angular displacement of said conduit with respect to saidreference plane, said displacement taking place about a precession axislying in said reference plane and perpendicular to said axis ofrotation, portions, of said loop having an undeflected position in saidreference plane, and all of said portions of said loop lying in saidreference plane parallel to said precession axis and displaced therefrombeing so constructed and arranged as to propagate fluid toward said axisof rotation.

3. In a gyroscopic flowmeter, a sensing conduit characterized by aplurality of fluid-carrying portions, some of said portions formed intoat least a loop lying in a reference plane of said conduit, means formounting said conduit for rotation about a first axis lying in saidreference plane, drive means for rotating said conduit about said firstaxis, the eflect of the flow of fluid in said conduit and of saidrotation of said conduit being to induce a prccessional torque tendingto deflect said loop about a precession axis lying in said referenceplane perpendicular to said first axis, and the configuration of all ofsaid loop portions lying substantially in said reference plane andparallel to said precession axis but displaced therefrom being such asto direct fluid toward said first axis.

4. In a gyroscopic flowmeter, a sensing conduit having a plurality ofportions arranged in series loops for carrying the fluid to be measured,means for supporting said conduit for rotation about an axis of rotationperpendicular to the axes of said loops, drive means for rotating saidconduit about said axis of rotation the combined effect of said fluidflow and said conduit rotation being a tendency for said conduit toprecess about an axis of precession perpendicular to said axis ofrotation and to said axes of said loops, said loops of said conduitbeing so constructed and arranged that one portion thereof carries saidfluid along said axis of precession while substantially all theremaining portions of said loops extending in the direction of said axisof precession carry said fluid toward said axis of rotation.

5. In a gyroscopic flowmeter, a sensing conduit according to claim 4 inwhich flexible couplings disposed sub stantially on said axis ofprecession are provided respectively to a fluid input line and a fluidoutput line, the effect of said flexible couplings being to permit someprecession of said conduit about said axis of precession.

6. In a gyroscopic flowmeter, a sensing conduit according to claim 4including gimbal means attached to said support means, and meansresiliently connecting said gimbal means to said sensing conduit topermit rotation about said axis of rotation and limited precession aboutsaid axis of precession.

7. A flowmeter comprising a sensing conduit characterized by a pluralityof fluid-carrying portions, at least some of said portions being formedinto loops lying in a reference plane of said conduit, means forsupporting said conduit for rotation about a first axis lying in saidreference plane, drive means for rotating said conduit about said firstaxis the effect of the flow of fluid in said conduit and of saidrotation of said conduit being to induce a precessional torque tendingto deflect said conduit about a precession axis lying in said referenceplane perpendicular to said first axis, and means for measuring thedeflection of said conduit from said reference plane, the configurationof all of said loop portions lying substantially in said reference planeand parallel to said precession axis but displaced therefrom being suchas to direct fluid toward said first axis.

8. A flowmeter comprising a length of conduit formed into at least twosubstantially coplanar serially connected loops, the axes of said loopsbeing parallel one to another, means for supporting said conduit forrotation about an axis of rotation which is perpendicular to the axes ofsaid loops, drive means for rotating said conduit about said axis ofrotation, means for introducing fluid into said conduit, means forextracting fluid from said conduit, said fluid following a path throughsaid loops between said introducing means and said extracting means, afirst flexible coupling between one of said loops and said introducingmeans, a second flexible coupling between the other of said loops andsaid extracting means, a gimbal ring connected at first oppositeperipheral points thereof to said support means substantially on saidaxis of rotation, torsion arms connected between second oppositeperipheral points of said gimbal ring and said coplanar loops, all saidperipheral points being equally spaced one from another about saidgimbal ring, and said second opposite peripheral points defining asecond axis, the configuration of said coplanar loops being such thatsubstantially all flow of fluid in a direction parallel to and displacedfrom said second axis in the plane of said axis of rotation is directedtoward said first axis, and means for measuring the displacement of saidcoplanar loops from said gimbal ring about said second axis caused bythe gyroscopic couple resulting from the flow of said fluid through saidconduit.

References Cited in the file of this patent UNITED STATES PATENTSPearson Jan. 6, 1953 OTHER REFERENCES

